As shown in FIG. 1, a chest building machine 1 of the prior art comprises two operation rods 2 and two curved handles 3 which are fastened with the operation rods 2 for holding fast with hands of an exerciser seated on a seat of the machine. As the handles 3 are pushed forward, the weights 4 are lifted by a steel cable for building the triceps of the upper arms and the pectoral muscle of the chest of the exerciser. Another prior art exercise machine 5 is shown in FIG. 2 and is mainly composed of a pull cord 6 which is connected at one end thereof with a cross rod which is provided with a handle 7 fastened therewith such that the weights 8 can be lifted by a cord fastened with the cross rod at the time when the handle 7 is gripped with hands of an exerciser to actuate the cross rod. The machine 5 is intended for building the latissimus dorsi and the humerus muscle. In addition, the operation rod 9 is provided with two handles 901 and 902 parallel to each other and perpendicular to the operation rod 9 for use in building muscles of specific parts of a human body. The handles 3, 901 and 902 of the prior art exercise machines 1 and 5 are fixed. As a result, one must use a variety of exercise machines to build the muscles of various parts of the body in view of the fact that the effect of the muscle-building exercise depends on the way that the hands grip the handles of the exercise machine.